Offset counterflow matrix fin for a counterflow plate-fin heat exchanger with crossflow headers

ABSTRACT

A heat exchanger includes a plurality of heat exchange cells positioned in a stacked configuration with respect to each other. Each cell includes first and second parting sheets, an internal finned member, and at least one external finned member. The first and second parting sheets include opposing first and second surfaces, an inlet manifold portion, an outlet manifold portion, an internal finned member portion and peripheral edges. The second parting sheet is substantially superimposed by, is spaced apart from and is coupled to the first parting sheet. The second surface of the second parting sheet confronts the second surface of the first parting sheet. The peripheral edges of the first and second parting sheets are attached to each other. The internal finned member is disposed between the second surfaces of the first and second parting sheets and has a leading edge positioned adjacent to the inlet manifold portion of the first and second parting sheets, and a trailing edge is positioned adjacent to the outlet manifold portion of the first and second parting sheets. The external finned member is attached to one of the first and second parting sheet. The external finned member has a leading edge and a trailing edge and is positioned offset from the internal finned member such that the leading edge of the external finned member outwardly extends beyond the leading edge of the internal finned member and the external finned member covers a portion of the inlet manifold member.

FIELD OF THE INVENTION

[0001] The present application is a continuation-in-part of U.S. patentapplication Ser. No. 09/409,641 filed Oct. 1, 1999, which is acontinuation of U.S. patent application Ser. No. 09/239,647 filed Jan.29, 1999 (U.S. patent No. 5,983,992), which is a continuation of U.S.patent application Ser. No. 08/792,261 filed Jan. 31, 1997 which, inturn, claims benefit under 35 U.S.C. Section 119(e) of U.S. ProvisionalApplication 60/010,998 filed Feb. 1, 1996. The disclosures set forth inU.S. patent application Ser. Nos. 09/409,641, 09/239,647, and 08/792,261and U.S. Provisional Application 60/010,998 are hereby incorporated byreference herein.

BACKGROUND OF THE INVENTION

[0002] This invention relates generally to plate-fin heat exchangers andmore particularly to a counter-flow plate-fin heat exchanger withcross-flow headers used as a recuperator. Plate fin heat exchangers aretypically monolithic structures created by brazing their manyconstituent pieces in a single furnace cycle. This general designpresents several problems including the following:

[0003] 1. A plate fin heat exchanger typically includes hundreds, if notthousands, of brazed joints. Thus, the overall quality of the finishedproduct depends on the reliability of each and every brazed joint sothat even one defective brazed joint can result in the entire heatexchanger being scrapped. As a result, assembly methods for plate finheat exchangers are generally labor intensive as assemblers must avoidthe creation of even a single poor braze among thousands in a typicalheat exchanger.

[0004] 2. The dimensions of the constituent parts used to assemble theheat exchanger must be maintained within close tolerances in order thatdifferences in thickness do not compound into gross differences in loadduring the brazing cycle.

[0005] 3. Edge bars or closure bars used to carry load through the edgesof the heat exchanger make assembly both labor and material intensiveand create stiffness and mass discontinuities antithetical to minimizingstrain during transient thermal operation.

[0006] With regard to the above design, counterflow plate-fin heatexchangers with cross-flow headers typically include a stack of headerssandwiched together to form an alternating gas/air/gas/air headerpattern. Each pair of adjacent gas and air headers is separated by arelatively thin parting sheet. Additionally, conventional plate-fin heatexchangers incorporate edge bars or closure bars to seal about theperimeters of the parting sheets and prevent overboard leakage from thehigh pressure side of the heat exchanger. Inlet and outlet manifoldducts are welded transverse to the edge bars after the headers areassembled and brazed. The edge bars create a stiff and massivestructural attachment between the parting sheets. Thermal loadingproduces faster thermal response in the lighter parting plates than themore massive edge bars. This difference in response time rate combinedwith the relative weakness of the parting plates can produce damage inthe parting plates. Due to differences in the position and structuralcomposition of the parting sheets and edge bars, the temperature changesdo not affect the bars and sheets at the same rate. Since the partingsheets are structurally weaker than the edge bars, the parting sheetsare strained.

[0007] A second problem associated with the use of edge bars incounterflow plate-fin heat exchangers is related to the sheet metalmanifold ducts that are welded to the edge bars. The manifolds arewelded to the stack of edge bars along the sides and comers of the coreadjacent the header openings. Like the parting sheets, the manifoldducts respond quickly to changes in temperature. Since the edge bars donot respond to changes in temperature as quickly as the manifold ducts,the sheet metal experiences a shear load at or near the weld. As aresult, the weld and the base metal in the heat affected zone is likelyto become damaged.

[0008] U.S. Pat. No. 2,858,112 to Gerstung discloses a cross-flow heatexchanger for transferring heat from a liquid (FIG. 1) in which multiplepairs 10 of corrugated plates 12 and 14 are spaced apart by aircentering means 16 and heat exchanger or edge bar elements 18 and 20.The edge bar elements 18 and 20 are sandwiched between the alignedheader openings 30 and 32 of the respective plates 12 and 14. Theutilization of the edge bar elements 18 and 20 adds undesirable rigidityand thermal mass discontinuity to the structure. As a result, thevarious layers of the structure are unable to move independently of oneanother during operation. Thus, the heat exchanger disclosed in theGerstung patent is not appropriate for use with a gas turbine becausethe exchanger cannot withstand the tremendous temperature extremesproduced by a gas turbine.

[0009] Great Britain Patent 1,304,692 to Lowery (FIGS. 1 and 5)discloses a cross-flow heat exchanger for transferring heat from aliquid including a plurality of metal plates 24 shaped and bondedtogether. The plates 24 have fin members 16 and 17 bonded to theirrespective outer surfaces. Each plate 24 has two centrally aperturedraised end portions 25 and 26 and also has two parallel invertedchannels 27 and 28. The respective units are assembled together byplacing the next unit in the sequence with its raised end portions 25and 26 in contact with equivalent raised end portions of the previousunit in the sequence, and by applying pressure to the juxtaposed pair ofraised end portions 25 and 26. The relatively large intermeshing surfaceareas of adjacent raised end portions 25 and 26 results in the formationof rigid flow ducts so that the various layers of the final structureare incapable of moving and flexing relative to one another.

[0010] Based on the foregoing limitations known to exist in presentplate-fin heat exchangers, it would be beneficial to provide a heatexchanger having a compliant bellows structure capable of elasticallyabsorbing deflections produced by temperature gradients attendant withthe heat exchange process and thermal gradients associated withinstallation or operation, so that the individual layers of the heatexchanger can move and flex freely relative to one another, and canaccommodate thermal deflections throughout of plane deformation. Itwould be advantageous to provide a heat exchange cell configured withgraduated stiffness at a transition section of the cell connecting thematrix to the cross-flow header to reduce damaging strain accumulationand to increase the fatigue life of the heat exchanger.

SUMMARY OF THE INVENTION

[0011] In accordance with certain preferred embodiments of the presentinvention, a heat exchanger for transferring heat between an externalfluid and an internal fluid includes two or more heat exchange cells.Each heat exchange cell preferably includes a top plate having an inletaperture at one end thereof and an outlet aperture at the other endthereof, the top plate including a first surface, a second surface andperipheral edges. The heat exchange cell may also include a bottom platejuxtaposed with the top plate having an inlet aperture at one endthereof and an outlet aperture at the other end thereof. The bottomplate also preferably includes a first surface, a second surface andperipheral edges, the peripheral edges of the bottom and top platesbeing attached to one another, whereby the second surfaces of the topand bottom plates confront one another and the inlet and outletapertures of the top and bottom plates are in substantial alignment withone another. The aligned inlet apertures and outlet apertures of therespective attached top and bottom plates preferably provide an inletmanifold on one side of the cell and an outlet manifold at the otherside of the cell. The inlet and outlet apertures of the top and bottomplates may include substantially S-shaped raised flange portionsextending away from the first surfaces of the plates, the substantiallyS-shaped raised flange portions terminating at interior edges boundingthe apertures. The attached top and bottom plates preferably define ahigh pressure chamber between the second surfaces thereof so that theinternal fluid may pass through the heat exchange cell at a higherpressure than the external fluid. The heat exchanger also preferablyincludes an internal finned member disposed within the high pressurechamber and attached to the second surfaces of said top and bottomplates. The individual heat exchange cells are preferably assembled oneatop the other with the adjacent interior edges of adjacent heatexchange cells attached together for forming a compliant bellowsstructure capable of elastically absorbing deflections produced duringthermal loading so that the heat exchange cells may move and flexrelative to one another.

[0012] In certain preferred embodiments, each heat exchange cellincludes an internal finned member and two external finned members, afirst one of the two external finned members being attached to the firstsurface of the top plate and a second one of the two external finnedmembers being attached to the first surface of the bottom plate. Eachheat exchange cell is designed for passing the external fluid throughthe two external finned members in a first flow direction and forpassing the internal fluid through the internal finned member in asecond flow direction substantially counter to the first flow direction.The internal fluid may be high pressure air passing through the internalfinned member and the external fluid may be a low-pressure productresulting from combustion. In other embodiments, the internal fluid maybe compressor discharge gases and the external fluid may be turbinedischarge gases. During operation of the heat exchange cell, the twoexternal finned members capture heat from the external fluid passingtherethrough and transfer the heat to the internal finned member. Theinternal finned member then transfers the heat to the internal fluidpassing therethrough.

[0013] Each top plate may include a substantially flat central regionbetween the inlet and outlet apertures thereof and the bottom platepreferably includes a substantially flat central region between theinlet and outlet apertures thereof, the substantially flat centralregions of the two plates being in substantial alignment with oneanother. In certain embodiments, the first one of the two externalfinned members overlies the substantially flat central region of the topplate, the second one of the two external finned members overlies thesubstantially flat central region of the bottom plate, and the internalfinned member is disposed between the substantially flat central regionsof the top and bottom plates. The internal finned member may be insubstantial alignment with the two external finned members. The internalfinned member is preferably brazed to the second surfaces of the top andbottom plates. In certain preferred embodiments, the first and secondexternal finned members of each heat exchange cell may includesubstantially aligned leading edges for receiving the external fluidpassing between the cell layers and trailing edges for discharging theexternal fluid after the external fluid has passed therethrough. Thesubstantially aligned leading edges of the first and second externalfinned members are desirably substantially remote from at least oneleading peripheral edge of the heat exchange cell for enabling theperipheral edge to deflect toward and away from a heat exchange celladjacent thereto. In other preferred embodiments, the substantiallyaligned leading edges of the first and second external finned membersare substantially offset from the aligned outlet apertures for enablingeach cell layer to deflect toward and away from a heat exchange celladjacent thereto. Offsetting the leading edges away from the bellowsstructure enables the bellows to flex and bend without being constrainedby the external finned members. Placing the leading edges of theexternal finned members away from the at least one leading peripheraledge also reduces thermal forces acting upon the top and bottom platesof each cell.

[0014] The trailing edges of the first and second external finnedmembers may also be in substantial alignment with one another, as wellas being substantially remote from at least one rear peripheral edge ofthe heat exchange cell for enabling the cell to move toward and awayfrom a heat exchange cell adjacent thereto. The substantially alignedtrailing edges of the first and second external finned members may alsobe substantially offset from the aligned inlet apertures of the heatexchange cell for enabling each cell to deflect toward and away from aheat exchange cell adjacent thereto. Each heat exchange cell may alsoinclude at least one gas turning finned member attached adjacent aperipheral edge of one of the plates for directing the external fluidinto a preferred path for impinging upon the two external finnedmembers.

[0015] As mentioned above, the internal finned member is desirablydisposed in the high pressure chamber of the cell and may have an inletedge for receiving the first gas from the inlet manifold and an outletedge for discharging the first gas to the outlet manifold. Each heatexchange cell may also include an inlet manifold finned member disposedin the high pressure chamber between the inlet manifold and the inletedge of the internal finned member and an outlet manifold finned memberdisposed in the high pressure chamber between the outlet manifold andthe outlet edge of the internal finned member. The inlet and outletmanifold finned members direct the internal fluid in a first directionand the internal finned member directs the internal fluid in a directionsubstantially perpendicular to the first direction. As mentioned above,heat is generally transferred between the external and internal fluidswhen the internal fluid passes through the internal finned member. Theinternal finned member of each cell is adhered to the top and bottomplates for providing resistance against differential pressure load sothat no external pre-loading of the heat exchange cell is required.

[0016] The top and bottom plates and the substantially S-shaped raisedflange portions thereof preferably have a substantially uniformthickness, thereby minimizing the effects of thermal expansion andcontraction on the plates. At the outer perimeter of the cell, thesubstantially S-shaped raised flange portions join together to partiallyform and define a high pressure chamber, while the inner edges of thesubstantially S-shaped raised flange portions, i.e., the edgessurrounding the inlet and outlet apertures of the attached plates,diverge from one another in each cell so that adjacent inner edges ofadjacent cells may be attached together. The adjacent interior edges ofthe adjacent cells are preferably welded together to form a compliantbellows structure. In highly preferred embodiments, the heat exchangecells are attached to one another solely through the interior edges ofthe raised flanges. In these embodiments, the sections of thesubstantially S-shaped raised flanges away from or remote from theinterior edges are not attached together. This enables the substantiallyS-shaped flange portions to independently move and flex in response tocompressive, tension and lateral forces.

[0017] The present invention also provides a heat exchanger fortransferring heat between an external fluid and an internal fluid. Theheat exchanger includes a plurality of heat exchange cells positioned ina stacked configuration with respect to each other. Each cell isconnected to at least one adjacent cell. Each cell includes first andsecond parting sheets, an internal finned member, and at least oneexternal finned member. The first parting sheet includes opposing firstand second surfaces, a first inlet header portion, a first outlet headerportion, a first internal finned member portion and peripheral edges.The second parting sheet is substantially superimposed by, is spacedapart from and is coupled to the first parting sheet. The second partingsheet includes opposing first and second surfaces, a second inlet headerportion, a second outlet header portion, a second internal finned memberportion and peripheral edges. The second surface of the second partingsheet confronts the second surface of the first parting sheet. At leasta portion of the peripheral edges of the first and second parting sheetsare attached to each other. The internal finned member is disposedbetween the second surfaces of the first and second parting sheets. Theinternal finned member is positioned at the first and second internalfinned member portions of the first and second parting sheets,respectively, and has a leading edge positioned adjacent to the firstand second inlet header portion of the first and second parting sheets,respectively, and a trailing edge positioned adjacent to the first andsecond outlet header portion of the first and second parting sheets,respectively. The at least one external finned member is attached to atleast one of the first surface of the first parting sheet and the firstsurface of the second parting sheet. The external finned member has aleading edge and a trailing edge. The external finned member ispositioned offset from the internal finned member such that the leadingedge of the external finned member outwardly extends beyond the trailingedge of the internal finned member.

[0018] The present invention also provides a heat exchange cell of aheat exchanger for transferring heat between an external fluid and aninternal fluid. The heat exchange cell includes first and second partingsheets, an internal finned member, at least one external finned member,and inlet and outlet headers. The first parting sheet includes opposingfirst and second surfaces, a first inlet header portion, a first outletheader portion and a first internal finned member portion. The secondparting sheet is substantially superimposed by, is spaced apart from andis coupled to the first parting sheet. The second parting sheet includesopposing first and second surfaces, a second inlet header portion, asecond outlet header portion, and a second internal finned memberportion. The second surface of the second parting sheet confronts thesecond surface of the first parting sheet. The internal finned member isdisposed between the second surfaces of the first and second partingsheets. The internal finned member has a leading edge and a trailingedge. The at least one external finned member is attached to at leastone of the first surface of the first parting sheet and the firstsurface of the second parting sheet. The external finned member has aleading edge and a trailing edge. The trailing edge of the internalfinned member extends along the juncture of the first and second outletheader portions to the first and second internal finned portions of thefirst and second parting sheets, respectively. The leading edge of theinternal finned member extends along the juncture of the first andsecond inlet header portions to the first and second internal finnedportions of the first and second parting sheets, respectively. Theexternal finned member is positioned offset from the internal finnedmember such that the leading edge of the external finned memberoutwardly extends beyond the leading edge of the internal finned member.

[0019] The foregoing and other aspects will become apparent from thefollowing detailed description of the invention when considered inconjunction with the accompanying FIGS.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 shows an exploded view of an individual heat exchange cellfor a counterflow heat exchanger in accordance with preferredembodiments of the present invention.

[0021]FIG. 2 shows a first plan view of the individual heat exchangecell shown in FIG. 1.

[0022]FIG. 3 shows an exploded view of the individual heat exchange cellof FIG. 1 after partial assembly thereof.

[0023]FIG. 4 shows an enlarged fragmentary view of an inlet header ofthe individual heat exchange cell shown in FIG. 2.

[0024]FIG. 5 shows a side view of a counterflow heat exchanger includinga plurality of the individual heat exchange cells shown in FIGS. 1-3.

[0025]FIG. 6 shows a perspective view of a counterflow heat exchangerincluding a plurality of the heat exchange cells shown in FIGS. 1-3, inaccordance with one preferred embodiment of the present invention.

[0026]FIG. 7 shows a partial cross-sectional view of the inlet aperturetaken along line 7-7 of FIG. 2, showing the raised flanges.

[0027]FIG. 8 shows a partial cross-sectional view of an edge of theindividual heat exchanger element shown in FIG. 2, taken along line 8-8,showing the details of a braze-reservoir.

[0028]FIG. 9 shows the flow of first and external fluids through theheat exchanger of FIG. 6 in accordance with certain preferredembodiments of the present invention.

[0029]FIG. 10 shows a perspective view of the heat exchange of FIG. 6after thermal loading whereby the structure flexes in response tothermal forces.

[0030]FIG. 11 shows a cross-sectional view of the heat exchanger shownin FIG. 9 taken along line XI-XI, before thermal loading.

[0031]FIG. 12 shows the heat exchanger of FIG. 11 after thermal loadingwhereby the structure flexes in response to thermal forces.

[0032]FIG. 13 shows a fragmentary top view of the heat exchanger shownin FIG. 9.

[0033]FIG. 14A shows a front view of the heat exchanger shown in FIG. 13along line XIV-XIV when the heat exchanger is in an undeflected “cold”state.

[0034]FIG. 14B shows a front view of the heat exchanger shown in FIG. 13along line XIV-XIV when the heat exchanger is in a deflected “hot”state.

[0035]FIG. 15 shows an exploded view of an individual heat exchange cellfor a counterflow heat exchanger in accordance with an embodiment of thepresent invention.

[0036]FIG. 16 is a sectional view an inlet manifold member, an internalfinned member and two external finned members of the heat exchange cellof FIG. 15.

[0037]FIG. 17 is a sectional view an outlet header, the internal finnedmember and the two external finned members of the heat exchange cell ofFIG. 15.

[0038]FIG. 18 is a graph illustrating the stiffness of the heat exchangecell along the portion of the heat exchange cell illustrated in FIG. 16

[0039]FIG. 19 shows an exploded view of an individual heat exchange cellfor a counterflow heat exchanger in accordance with another preferredembodiment of the present invention.

[0040]FIG. 20 is a sectional view an outlet header, the internal finnedmember and the two external finned members of the heat exchange cell ofFIG. 19.

[0041]FIG. 21 is a graph illustrating the stiffness of the heat exchangecell along the portion of the heat exchange cell illustrated in FIG. 20.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042]FIG. 1 shows an exploded view of an individual heat exchange cell10 in accordance with certain preferred embodiments of the presentinvention. Each heat exchange cell 10 includes a self-containedpressure-tight structure which may be stacked atop other substantiallyidentical heat exchange cells to produce a counterflow heat exchanger,such as the exchanger shown in FIG. 9 and described below. Each heatexchange cell 10 has all of the features required for providing acomplete counterflow heat exchanger including inlet and exit manifoldsand heat transfer fins assembled into a single unit cell, as shown inFIG. 2.

[0043] The utilization of individual heat exchange cells overcomes thefollowing problems present in the prior art:

[0044] 1) Allows for the inspection, correction and/or rejection of asmall, manageable heat exchange cell rather than on a completed heatexchanger comprising a matrix of permanently assembled layers, therebyresulting in greater quality control and reduced scrap.

[0045] 2) Allows for quality-control testing of individual heat exchangecells before the various layers are assembled together, thereby avoidingthe risk and technical difficulty of brazing massive heat exchangermatrices.

[0046] 3) Allows for slip and movement between layers to accommodate forthermal expansion and contraction, without the risk of leakage.

[0047] 4) Allows for the rapid removal and replacement of defective heatexchange is cells, as opposed to scrapping an entire heat exchanger whena defective layer is discovered.

[0048] Referring to FIGS. 1 and 2, in certain preferred embodiments,each individual heat exchange cell 10 preferably includes a top plate 12having a first surface 14, a second-surface 16 (FIG. 5) and one or moreperipheral edges 18 defining outer edge(s) of the top plate 12. The topplate 12 preferably includes an inlet aperture 20A at one end thereof,an outlet aperture 22A at the other end thereof and a substantially flatcentral region 24A between the inlet and outlet apertures 20A and 22A.Each heat exchange cell 10 also preferably includes a bottom plate 26that substantially mirrors the dimensions, size and shape of the topplate 12. The bottom plate 26 preferably has a first surface 28 (FIG.6), a second surface 30 and one or more peripheral edges 32 definingouter edge(s) of the bottom plate 12. The bottom plate 26 alsopreferably includes an inlet aperture 20B at one end thereof, an outletaperture 22B at the other end thereof and a substantially flat centralregion 24B (FIG. 5) between the inlet and outlet apertures 20B and 22B.

[0049] The heat exchange cell 10 preferably includes at least one finnedmember attached thereto for transferring heat between two or more fluidspassing closely by one another. In one particular embodiment, the heatexchange cell 10 preferably includes two external finned members, afirst one of the external finned members 34A attached to the firstsurface 14 of the top plate 12, preferably within the substantially flatcentral region 24A thereof; and a second one of the two external finnedmembers 34B attached to the first surface 28 of the bottom plate 26,preferably within the substantially flat central region 24B thereof.

[0050] The heat exchange cell 10 is preferably assembled by juxtaposingthe second surfaces 16,30 of the top and bottom plates 12, 26 with oneanother so that the inlet apertures 20A, 20B and the outlet apertures22A, 22B of the top and bottom plates 12 and 26 are in substantialalignment. The inlet apertures 20A, 20B include respective substantiallyS-shaped raised flange portions 36A and 36B terminating at interioredges bounding the inlet apertures 20A, 20B. Similarly, the outletapertures 22A, 22B include respective substantially S-shaped raisedflange portions 38A, 38B terminating at interior edges bounding theoutlet apertures 22A, 22B. In other words, the substantially S-shapedraised flange portions of the attached top and bottom plates 12 and 26diverge from one another at the interior edges thereof and are joined atthe outer peripheral edges of the plates. Thus, each substantiallyS-shaped raised flange portion generally extends away from the firstsurface of the plate associated therewith so that the interior edgethereof lies above the first surface of the plate. In preferredembodiments, the top and bottom plates 12, 26 including the respectivesubstantially S-shaped raised flange portions thereof are ofsubstantially uniform thickness so that temperature changes occurring atthe flanges are substantially the same as temperature changes occurringalong the remainder of the top and bottom plates 12, 26, whereby thermalstrain produced during operation of the heat exchanger is minimized.

[0051] The peripheral edges 18, 32 of the respective top and bottomplates 12 and 26 are then attached to one another, whereby the alignedinlet apertures 20A, 20B of the attached top and bottom plates 12 and 26provide an inlet manifold of the heat exchange cell 10 and the alignedoutlet apertures 22A, 228 of the attached top and bottom plates providean outlet manifold of the heat exchange cell 10. The attached top andbottom plates 12, 26 define a high pressure chamber 52 (FIG. 5) betweenthe second surfaces thereof so that a fluid may pass therethrough at arelatively higher pressure than do fluids passing over the firstsurfaces of the plates.

[0052] The heat exchange cell 10 also preferably includes an internalfinned member 40 disposed between and attached to the second surfaces ofthe top and bottom plates 12, 26. The internal finned member 40 ispreferably brazed to the second surfaces 16, 30 of the top and bottomplates 12, 26. When the cell is assembled, the internal finned member 33is typically in substantial vertical alignment with the two externalfinned members 34A, 34B, the two external finned members also being insubstantial vertical alignment with one another.

[0053] Referring to FIG. 3, each heat exchange cell 10 is preferablyadapted for passing an internal fluid, such as a combustible gas,through the internal finned member 40 in a first flow directiondesignated 56 and for passing an external fluid, such as an exhaust gas,through the two external finned members 34 in a second flow directiondesignated 54 that is substantially counter to the first flow direction54.

[0054] Referring to FIGS. 1-3, the internal finned member 33 attached tothe second surfaces of the top and bottom plates 12 and 26 desirablyincludes an inlet end 42 for receiving the internal fluid from the inletmanifold 20 and an outlet end 44 for discharging the internal fluid tothe outlet manifold 22. The heat exchange cell 10 may also include aninlet manifold finned member 46 disposed in the high pressure chamberbetween the inlet manifold 20 and the inlet edge 42 of the internalfinned member 33 and an outlet manifold finned member 48 disposed in thehigh pressure chamber between the outlet edge 44 of the internal finnedmember 33 and the outlet manifold 22. As shown in FIG. 3, the inlet andoutlet manifold finned members 46, 48 direct the internal fluid in firstlateral or cross-flow directions 58A, 58B and the internal finned member33 directs the external fluid in the direction designated 56 that issubstantially perpendicular to the first lateral directions 58A, 58B.

[0055]FIG. 4 shows a fragmentary, close-up view of the inlet manifold20, inlet manifold finned member 46 and internal finned member 33 of apreferred heat exchange cell 10. In this embodiment, the inlet manifoldfinned member 46 includes a series of channels 50 which serve asconduits for passing the internal fluid from the inlet manifold 20 tothe first edge 42 of the internal finned member 33. In preferredembodiments, each channel 50 is in fluid communication with a pluralityof channels 52A, 52B, 52C of the internal finned members 33. Referringto FIG. 8, in certain embodiments the inlet manifold fins 46 (or theoutlet manifold fins) may terminate at the portion of the top and bottomplates 12 and 26 where the plates diverge to form substantially S-shapedraised flanges 36A, 36B. This termination configuration is shown insolid font in FIG. 7. Alternatively, the inlet manifold fins may extendbeyond the portion of divergence of the plates 12, 26 in the mannershown in FIG. 7 by dashed font designated 46.

[0056] Referring to FIGS. 5 and 6, in preferred embodiments, a heatexchanger 60 is provided by assembling two or more heat exchange cells10 one atop the other with the adjacent interior edges of adjacent heatexchange cells attached together for forming a compliant bellowsstructure 62 capable of elastically absorbing deflections producedduring thermal loading so that the individual heat exchange cells maymove relative to one another. For example, FIG. 5 shows a heat exchangerincluding stacked heat exchange cells 10A, 10B, 10C and 10D. Heatexchange cell 10A includes top plate 12A having substantially S-shapedraised flange portion 36A with interior edge 64A and bottom plate 26Ahaving substantially S-shaped raised flange portion 36B with interioredge 64B. Heat exchange 10B is substantially similar to heat exchangecell 10A and also includes interior edges 64A and 64B. The heat exchangecells 10A and 10B are attached together solely through the adjacentinterior edges (e.g., such as by welding the interior edge 64A of heatexchange cell 10B with the interior edge 64A of heat exchange cell 10B).The portions of the substantially S-shaped raised flanges 36 remote fromthe interior edges 64 are not attached to an adjacent heat exchangecell. This allows the substantially S-shaped raised flanges to flex inresponse to compression and tension forces. The process is continueduntil the heat exchange cells 10A-10D are attached together through theadjacent interior edges.

[0057] The external finned members 34 of adjacent heat exchange cells 10are not attached or bonded together so that the individual heat exchangecells are free to move relative to one another during heating up andcooling down of the heat exchanger. As mentioned above, the weldedinterior edges of the substantially S-shaped raised flanges form acompliant bellows structure capable of elastically absorbing deflectionsproduced during thermal loading so that the individual heat exchangecells may move relative to one another. The compliant nature of thebellows structure minimize stresses and strains placed upon the heatexchanger structure.

[0058] In addition, prior art heat exchangers typically include gasheader fins adjacent the external finned members 34 attached to the topand bottom plates. The gas header fins are typically provided for 1)directing flow into the heat exchanger matrix; 2) providing compressivestrength to react pressure; and 3) providing a continuous load pathbetween the layers during assembly and manufacturing. The presentinvention does not require such gas header fins due, inter alia, to thefact that each individual cell is pressure balanced (i.e., includes itsown internal high pressure chamber so that each individual heat exchangecell may function, if necessary, as a complete heat exchanger). Thus,the absence of gas header fins from the individual heat exchange cellsof the present invention provides numerous benefits including providingflexibility to the cell that enables the cell to deflect out-of-planeand thus respond to thermal gradients.

[0059] Referring to FIG. 9, during operation of one preferred embodimentof the heat exchanger 60, the external fluid, such as a heated exhaustgas, travels in the direction designated 54 and through the externalfinned members 34 of the stacked heat exchange cells 10. At the sametime, the internal fluid, such as a relatively cool compressor dischargeair travels through the compliant inlet manifold structure 62 in adownward direction designated 66. Referring to FIG. 3, the internalfluid then passes in succession though the inlet manifold finned member58A, the internal finned member 33 and the outlet manifold finned member58B. At least some of the heat present in the external fluid istransferred to the internal fluid as the heat is transferred from theexternal finned members to the internal finned member. Referring to FIG.9, the internal fluid then passes from the outlet manifold finnedmembers of the respective cells 10 to the outlet manifold structure 68in the direction designated 70. The temperature of the internal fluiddischarged from the heat exchanger 60 is typically higher than thetemperature of the internal fluid entering the heat exchanger. Referringto FIG. 10, the compliant nature of the inlet and outlet manifolds andthe individual plates enables the cells of the heat exchanger to moverelative to one another during operation so as to minimize the adverseaffects that may result from thermal expansion and contraction. Duringoperation, there is no need to apply external forces to the outside ofeach heat exchange cell 10 in order to hold the cell together because,inter alia, the internal finned member 33 is fully adhered to the topand bottom plates 12, 26 (which provides resistance against differentialpressure load).

[0060] Referring to FIGS. 1, 2 and 13, in certain preferred embodimentsthe first and second external finned members 34A and 51B of each heatexchange cell may include substantially aligned leading edges 72A and89B that are desirably adapted for receiving the external fluid passingbetween the cell layers. The first and second external finned membersmay also include trailing edges 74A and 91B adapted for discharging theexternal fluid therefrom after the external fluid has passed completelythrough the external finned members. The substantially aligned leadingedges 72A and 89B of the first and second external finned members 34Aand 51B are desirably substantially remote from a leading peripheraledge 76 of the heat exchange cell 10. In other words, Referring to FIG.11, there exists a space or gap 78 between the aligned leading edges 72Aand 89B of the external finned members and the leading peripheral edge76 of the heat exchange cell 10. The space 78 enables the individualcells to move toward and away from one another. Referring to FIG. 2, thesubstantially aligned leading edges 72A and 89B of the first and secondexternal finned members 34A and 51B may also be substantially offsetfrom the aligned outlet apertures 22 forming the flexible outletmanifold structure 68 for also enabling each cell to deflect toward andaway from a heat exchange cell adjacent thereto.

[0061] Referring to FIGS. 1, 2 and 13, in other preferred embodiments,the trailing edges 74A and 91B of the first and second external finnedmembers 34A and 51B may also be in substantial alignment with oneanother and substantially remote from a rear peripheral edge 80 of theheat exchange cell 10. There preferably exists a space or gap 82 betweenthe trailing edge 74A of the external finned member 34 and the rearperipheral edge 80 of the cell for enabling each individual cell todeflect toward and away from a heat exchange cell adjacent thereto. Thesubstantially aligned trailing edges 74A and 91B of the first and secondexternal finned members 34A and 51B are substantially offset from thealigned inlet apertures 20 forming the flexible inlet manifold structure62 of the heat exchanger 60 for enabling each cell to deflect toward andaway from a heat exchange cell adjacent thereto.

[0062]FIG. 11 shows a fragmentary cross-sectional view of the heatexchanger shown in FIG. 9 before the bellows structures have flexedand/or bowed in response to thermal forces. The various cell layers aresubstantially parallel to one another because, inter alia, the heatexchanger is not under thermal stress. The leading edges 72A and 89B ofthe external finned members 34A and 51B are remote from the leadingperipheral edge 76 of the cell, thereby providing a gap 78 that extendsbetween the adjacent cell layers. FIG. 12 shows a fragmentarycross-sectional view of the heat exchanger of FIG. 9 after thermalloading whereby the heat exchanger flexes, bends and/or deflects inresponse to thermal forces. The leading peripheral edges 76 of therespective cell layers are able to move toward one another because thegaps 78 provide room into which the respective cell layers are able tomove toward one another because the gaps 78 provide room into which therespective cell layers may move, thereby providing the heat exchangerwith enhanced flexibility.

[0063]FIG. 13 shows a top fragmentary view of the heat exchanger 60shown in FIGS. 9 and 14. FIGS. 14A and 14B show a front view of the heatexchanger 60 taken along line XIV-XIV of FIG. 13. FIG. 14A shows theheat exchanger in an undeflected “cold” state, i.e., before the celllayers 10 have flexed and/or bowed in response to thermal forces. Asshown in FIG. 14A, the leading edges 76 of the various cell layers 10are substantially flat and parallel to one another. FIG. 14B shows theheat exchanger in a deflected “hot” state, i.e., after the leading edges76 of the respective cell layers 10 have flexed and/or bowed in responseto thermal forces. As shown in FIG. 14B, at least some of the leadingedges 76 have flexed and/or deflected away from cell layers 10 adjacentthereto. As mentioned above, the leading peripheral edges 76 of therespective cell layers 10 are able to deflect toward and away fromadjacent cell layers because the leading edges 76 are remote from theleading edges 72 of the external finned members 74 for forming form gaps78 in which the respective cell layers 10 may move and/or deflect,thereby providing the heat exchanger 60 with enhanced flexibility.

[0064] In one preferred method of assembling individual heat exchangecells 10, the top and bottom plates 12, 26 (also known as partingplates) are formed from .010-.050 inch stainless or super alloy steelsheet in roll form. The sheet is unrolled and then the plates are formedby stamping and laser trimming. The external finned members 34 and gasis turning fins 52 are formed from .003-.010 inch rolled stainless orsuper alloy steel. The metal is unrolled, the fins are folded and brazecoating is sprayed onto one side of the external finned member 34 andthe gas turning fin 52. The braze coated external finned member 34 andgas turning fin 52 are then laser trimmed and cleaned. Instead ofapplying a braze coat to the external finned member 34 and gas turningfin 52, the first surfaces 14, 28 of the respective top and bottomplates 12, 26 may be coated with the braze coating. The internal finnedmember 33 and the inlet and outlet manifold finned members 46, 48 areformed from .003-.010 inch rolled stainless or super alloy steel. Themetal is unrolled, the fins are folded and braze coating is sprayed ontoboth sides of the internal finned member 33 and the inlet and outletmanifold finned members 46, 48. The braze coated internal finned member33 and inlet and outlet manifold finned members 46, 48 are then lasertrimmed and cleaned. Instead of applying a braze coat to the internalfinned member 33 and the inlet and outlet manifold finned members 46,48, both inside surfaces of the top and bottom plates 12, 26 may bebraze coated.

[0065] The top and bottom plates 12, 26; the two external finned members34A, 34B; the internal finned member 33; and the inlet and outletmanifold finned members 46, 48 are assembled to form an individual heatexchange cell 10. The individual pieces are tack welded to temporarilyhold the pieces together. In addition, the peripheral edge of theassembled individual heat exchange cell 10 may be laser welded.

[0066] One or more assembled individual heat exchange cells 10 are thenpreferably placed into a braze cell where the individual cells 10 areheated to braze the coated surfaces to one another. Various brazing jigcomponents can be used to load the individual heat exchange cells 10 tominimize any distortion of the cells 10 during the brazing process.FIGS. 7 and 8 illustrate a preferred embodiment of the top and bottomplates 12, 26, including a reservoir 54 provided in top plate 12. Thisreservoir 54 holds additional braze coating which will spread in theadjacent surfaces of the interior of an individual heat exchange cell 10during the brazing process.

[0067] After brazing, each heat exchange cell 10 is pressurized to checkfor any leaks caused by inadequate brazing. A plurality of individualheat exchange cells 10 are then assembled into a partial stack and theinterior edges of the substantially S-shaped raised flanges 36, 38 arewelded together. These partial stacks are then pressure tested again. Aplurality of partial stacks are then welded together to provide a heatexchanger. Transition pieces (not shown) may be attached to outerindividual heat exchange cells 10 to provide a place to connect the heatexchanger to the inlet and outlet manifolds of the equipment the heatexchanger is a part of.

[0068]FIG. 15 shows an exploded view of an individual heat exchange cell100 in accordance with a preferred embodiment of the present invention.Each individual heat exchange cell 100 preferably includes a firstparting sheet 102 having one or more peripheral edges 117 defining outeredge(s) of the first parting sheet 102. The first parting sheet 102preferably includes an inlet aperture 160A at one end thereof, an outletaperture 162A at the other end thereof and a substantially flat centralregion 164A between the inlet and outlet apertures 160A and 162A. Eachheat exchange cell 100 also preferably includes a second parting sheet104 that substantially mirrors the dimensions, size and shape of thefirst parting sheet 102. The second parting sheet 104 preferably has oneor more peripheral edges 166 defining outer edge(s) of the secondparting sheet 104. The second parting sheet 104 also preferably includesan inlet aperture 160B at one end thereof, an outlet aperture 162B atthe other end thereof and a substantially flat central region 164Bbetween the inlet and outlet apertures 160B and 62B.

[0069] The heat exchange cell 100 preferably includes two externalfinned members, a first external finned member 108 attached to the firstparting sheet 102 preferably within the substantially flat centralregion 164 thereof; and a second external finned member 110 attached tothe second parting sheet 104, preferably within the substantially flatcentral region 164B thereof. The peripheral edges 117, 166 of therespective first and second parting sheets 102, 104 are attached to oneanother, whereby the aligned inlet apertures 160A, 160B of the attachedfirst and second parting sheets 102, 104 provide an inlet manifold 160of the heat exchange cell 100 and the aligned outlet apertures 162A,162B of the attached first and second parting sheets 102, 104 provide anoutlet manifold 162 of the heat exchange cell 100.

[0070] The heat exchange cell 100 also preferably includes an internalfinned member 106 disposed between and attached to the first and secondparting sheets 102, 104. When the cell is assembled, the internal finnedmember 106 is typically in substantial vertical alignment with the twoexternal finned members 108, 110, the two external finned members 108,110 also being in substantial vertical alignment with one another.

[0071] The internal finned member 106 preferably includes a leading edge126 for receiving the internal fluid from the inlet manifold 160 and atrailing edge 128 for discharging the internal fluid to an outletmanifold 162. The heat exchange cell 10 may also include an inlet header127 disposed in the high pressure chamber between the inlet manifold 160and the leading edge 126 of the internal finned member 106 and an outletheader 129 disposed in the high pressure chamber between the trailingedge 128 of the internal finned member 106 and the outlet manifold 162.The inlet and outlet headers 127, 129 direct the internal fluid in firstlateral or cross-flow directions and the internal finned member 106directs the external fluid in the direction that is substantiallyperpendicular to the first lateral directions.

[0072] Heat exchange cell 100 is configured for transferring heatbetween an external fluid and an internal fluid. In an exemplaryembodiment, heat exchange cell 100 is a counter-flow heat exchange cellconfigured for enabling an internal fluid to pass through an interiorfinned heat exchange section of heat exchange cell 100 in a firstdirection and enable an external fluid to pass through exterior finnedheat exchange section of heat exchange cell 100 in a direction generallyopposite that of the internal fluid. In an exemplary embodiment, heatexchange cell 100 is a cross-flow cell wherein the internal fluid isdirected along an inlet region of heat exchange cell 100 in a seconddirection and then is redirected in the first direction substantiallyperpendicular, or oblique, to the second direction and along the flowpath defined by the interior finned section of heat exchange cell 100.Upon exiting the interior finned sections of heat exchange cell 100 theflow of the internal fluid is redirected again in a third directionwhich is substantially perpendicular, or oblique, to the firstdirection.

[0073]FIGS. 16 and 18 illustrate sectional views of an individualcross-flow heat exchange cell 100 in accordance with an exemplaryembodiment of the present invention. FIG. 16 illustrates the inletregion of heat exchange cell 100 for directing the flow of an internalfluid. FIG. 18 illustrates the outlet region of heat exchange cell 100for directing the flow of the internal fluid. Heat exchange cell 100includes the first and second parting sheets 102, 104, the internalfinned member 106, and the first and second external finned members 108,110. First and second parting sheets 102, 104 are generally flat plateseach having opposing first and second surfaces 116, 118, 120, 122 andperipheral edges. Second surface 120 of second parting sheet 104confronts or faces second surface 118 of first parting sheet 102. Aportion of the peripheral edges of first and second members 102, 104 areconnected to each other to form a chamber 124. First and second partingsheets 102; 104 are connected to and retain internal finned member 106between second surfaces 118, 120 and within chamber 124. First andsecond parting sheets 102, 104, between second surfaces 118, 120, alsoconnect to the inlet header 127 and to the outlet header 129. Firstsurface 116 of first parting sheet 102 connects to first external finnedmember 108 and first surface 122 of second parting sheet 104 connects tosecond external finned member 110. First and second parting sheets 102,104 include inlet and outlet apertures 160, 162 (see FIG. 15) and areconfigured to define a flow path for an internal fluid.

[0074] Internal finned member 106 is a segment of fin stock. Internalfinned member 106 includes a leading edge 126 and a trailing edge 128.Internal finned member 106 is connected to and between second surfaces118, 120 of first and second parting sheets 102, 104. In an exemplaryembodiment, internal finned member 106 is brazed to second surfaces 118,120 of first and second parting sheets 102, 104. The connection ofinternal finned member 106 to first and second parting sheets 102, 104at internal finned portion 138, 140 of first and second parting sheets.Internal finned member 106 is configured to create passages of arequisite hydraulic diameter for directing the flow of an internalfluid, to increase heat transfer area of heat exchange cell 100, and toprovide structural support to heat exchange cell 100.

[0075] First and second external finned members 108, 110 are segments offin stock. First and second external finned members 108, 110 includefirst and second trailing edges 130, 132 and first and second leadingedges 134, 136. First external finned member 108 is attached to firstsurface 116 of first parting sheet 102 and second external finned member110 is attached to first surface 122 of second parting sheet 104. Firstand second external finned members 108, 110 generally have the same plandimensions as internal finned member 106. Internal and external finnedmembers 106, 108, 110 are separated by first and second parting sheets102, 104 and are stacked with respect to one another with leading edge126 and trailing edges 130, 132 in general alignment with one another,and trailing edges 128 and leading edges 134, 136 in general alignmentwith one another. First and second external finned members 108, 110 areconfigured to create passages of a requisite hydraulic diameter fordirecting the flow of an external fluid, to increase heat transfer areaof heat exchange cell 100, and to provide structural support to heatexchange cell 100. In an exemplary embodiment, internal finned member106 is configured to direct the flow of an internal fluid generallyalong a first plane in a first direction and each external finned member108, 110 is configured to direct the flow of an external fluid in adirection opposite the first direction. In alternative exemplaryembodiments, heat exchange cell 100 can include a single external finnedmember connected to one of first surface 114 of first parting sheet 102and first surface 120 of second parting sheet 104.

[0076] Referring to FIG. 16, the inlet header 127 is a finned cross-flowheader. The inlet header 127 is positioned between and connected tofirst and second parting sheets 102, 104. Inlet header 127 is comprisedof more coarsely configured fins than internal and external finnedmembers 106, 108, 110. The inlet header 127 is positioned adjacent tothe internal finned member 106 at leading edge 126. The inlet header 127is configured to deliver an internal fluid from inlet aperture 160 (seeFIG. 15) to internal finned member 106. The inlet header 127 directs theflow of an internal fluid generally along the first plane in a seconddirection that is substantially perpendicular, or oblique, to thedirection of internal fluid flow through internal finned member 106,referred to as the first direction.

[0077] Referring to FIG. 18, the outlet header 129 is a finnedcross-flow header. The outlet header 129 is positioned between andconnected to first and second parting sheets 102, 104. Outlet manifoldfinned member 129 is comprised of more coarsely configured fins thaninternal and external finned members 106, 108, 110. Outlet header 129 ispositioned adjacent to the internal finned member 106 at trailing edge128. The outlet header 129 is configured to collect an internal fluidfrom internal finned member 106 and deliver the flow to outlet aperture162 (see FIG. 15). The outlet header 129 directs the flow of an internalfluid generally along the first plane in a third direction that issubstantially perpendicular, or oblique, to the first direction.

[0078]FIGS. 16 and 18 further illustrate the transition of inlet andoutlet headers 127, 128 to the internal finned portions 106, otherwisereferred to as a transition region 144. FIG. 17 illustrates the relativestiffness of heat exchange cell 100 along the section of heat exchangecell 100 illustrated in FIG. 16. As illustrated in FIG. 17, theexemplary embodiment of heat exchange cell 100 of FIG. 16 includes asharp drop in stiffness at the connection of internal and externalfinned portions 106, 108, 110 of heat exchange cell 100 to transitionregion 144, and an sharp increase in stiffness from transition region144 to the outlet header 129.

[0079]FIG. 19 shows an exploded view of an individual heat exchange cell200 in accordance with a preferred embodiment of the present invention.Each individual heat exchange cell 200 preferably includes a firstparting sheet 202 having one or more peripheral edges 217 defining outeredge(s) of the first parting sheet 202. The first parting sheet 202preferably includes an inlet aperture 260A at one end thereof, an outletaperture 262A at the other end thereof and a substantially flat centralregion 264A between the inlet and outlet apertures 260A and 262A. Eachheat exchange cell 200 also preferably includes a second parting sheet204 that substantially mirrors the dimensions, size and shape of thefirst parting sheet 202. The second parting sheet 204 preferably has oneor more peripheral edges 266 defining outer edge(s) of the secondparting sheet 204. The second parting sheet 204 also preferably includesan inlet aperture 260B at one end thereof, an outlet aperture 262B atthe other end thereof and a substantially flat central region 264Bbetween the inlet and outlet apertures 260B and 262B.

[0080] The heat exchange cell 200 preferably includes two externalfinned members, a first external finned member 208 attached to the firstparting sheet 202, preferably within the substantially flat centralregion 264 thereof; and a second external finned member 210 attached tothe second parting sheet 204, preferably within the substantially flatcentral region 264B thereof. The peripheral edges 217, 266 of therespective first and second parting sheets 202, 204 are attached to oneanother, whereby the aligned inlet apertures 260A, 260B of the attachedfirst and second parting sheets 202, 204 provide an inlet manifold 260of the heat exchange cell 200 and the aligned outlet apertures 262A,262B of the attached first and second parting sheets 202, 104 provide anoutlet manifold 262 of the heat exchange cell 200.

[0081] The heat exchange cell 200 also preferably includes an internalfinned member 206 disposed between and attached to the first and secondparting sheets 202, 204. The two external finned members 208, 210 alsobeing in substantial vertical alignment with one another.

[0082] The internal finned member 206 attached preferably includes aleading edge 226 for receiving the internal fluid from the inletmanifold 260 and a trailing edge 228 for discharging the internal fluidto an outlet manifold 262. The heat exchange cell 10 may also include aninlet header 227 disposed in the high pressure chamber between the inletmanifold 260 and the leading edge 226 of the internal finned member 206and an outlet header 229 disposed in the high pressure chamber betweenthe trailing edge 228 of the internal finned member 206 and the outletmanifold 262.

[0083] Heat exchange cell 200 is configured for transferring heatbetween an external fluid and an internal fluid. In an exemplaryembodiment, heat exchange cell 200 is a counter-flow heat exchange cellconfigured for enabling an internal fluid to pass through an interiorfinned heat exchange section of heat exchange cell 200 in a firstdirection and enable an external fluid to pass through exterior finnedheat exchange section of heat exchange cell 200 in a direction generallyopposite that of the internal fluid. In an exemplary embodiment, heatexchange cell 200 is a cross-flow cell wherein the internal fluid isdirected along an inlet region of heat exchange cell 200 in a seconddirection and then is redirected in the first direction substantiallyperpendicular, or oblique, to the second direction and along the flowpath defined by the interior finned section of heat exchange cell 200.Upon exiting the interior finned sections of heat exchange cell 200 theflow of the internal fluid is redirected again in a third directionwhich is substantially perpendicular, or oblique, to the firstdirection.

[0084]FIG. 20 illustrates a sectional view of the cross-flow heatexchange cell 200 in accordance with an alternative exemplary embodimentof the present invention. FIG. 20 illustrates the outlet region of heatexchange cell 200 for directing the flow of the internal fluid. Heatexchange cell 200 includes first and second parting sheets 202, 204, theinternal finned member 206, and first and second external finned members208, 210. First and second parting sheets 202, 204 are generally flatplates each having opposing first and second surfaces 216, 218, 220, 222and peripheral edges. Second surface 220 of second parting sheet 204confronts or faces second surface 218 of first parting sheet 202. Aportion of the peripheral edges of first and second members 202, 204 areconnected to each other to form a chamber 224. First and second partingsheets 202, 204 are connected to and retain internal finned member 206between second surfaces 218, 220 and within chamber 224. First andsecond parting sheets 202, 204, between second surfaces 218, 220, alsoconnect to the inlet and outlet header 227, 229.

[0085] First surface 216 of first parting sheet 202 connects to firstexternal finned member 208 and first surface 222 of second parting sheet204 connects to second external finned member 210. First and secondparting sheets include inlet and outlet apertures 260, 262 (see FIG. 19)and are configured to define a flow path for an internal fluid. Firstand second parting sheets 202, 204 therefore each include an internalfinned member portion connected to internal finned member 206. Firstsurface 216 of first parting sheet 202 further connects to firstexternal finned member 208 and first surface 222 of second parting sheet204 connects to second external finned member 210. In an alternativeexemplary embodiment, the first and second parting sheets each includean internal finned member portion which connects to an inlet headersheet portion and an outlet header sheet portion, respectively. Thetrailing edges of the internal finned member extend along the junctureof the first and second outlet header sheet portions to the internalfinned member portion of the first and second parting sheets.

[0086] Internal finned member 206 is a segment of fin stock. Internalfinned member 206 includes a leading edge 226 (see FIG. 19) and atrailing edge 228. Internal finned member 206 is connected to and isdisposed between second surfaces 218, 220 of first and second partingsheets 202, 204. In an exemplary embodiment, internal finned member 206is brazed to second surfaces 218, 220 of first and second parting sheets202, 204. The connection of internal finned member 206 to first andsecond parting sheets 202, 204 at an internal finned portion 238, 240 offirst and second parting sheets 202, 204. Internal finned member 206 isconfigured to create passages of a requisite hydraulic diameter fordirecting the flow of an internal fluid, to increase heat transfer areaof heat exchange cell 200, and to provide structural support to heatexchange cell 200. In an exemplary embodiment, internal finned member206 includes convolutions.

[0087] First and second external finned members 208, 210 are segments offin stock. First and second external finned members 208, 220 includefirst and second leading edges 230, 232 and first and second trailingedges 234, 236. First external finned member 208 is attached to firstsurface 216 of first parting sheet 202 and second external finned member210 is attached to first surface 222 of second parting sheet 204. Firstand second external finned members 208, 210 are configured to createpassages of a requisite hydraulic diameter for directing the flow of anexternal fluid, to increase heat transfer area of heat exchange cell200, and to provide structural support to heat exchange cell 200. In anexemplary embodiment, internal finned member 206 is configured to directthe flow of an internal fluid generally along a first plane in a firstdirection and each external finned member 208, 210 is configured todirect the flow of an external fluid in a direction opposite the firstdirection. In alternative exemplary embodiments, heat exchange cell 200can include a single external finned member connected to one of firstsurface 216 of first parting sheet 202 and first surface 222 of secondparting sheet 204. In an exemplary embodiment, first and second externalfinned members 208, 210 further include convolutions.

[0088] The interface between a counter-flow matrix (internal andexternal finned members separated by parting sheets of a heat exchangecell of a heat exchanger) and cross-flow headers of a plate-fin heatexchanger can be susceptible to damage due to discontinuities ofstiffness and thermal response. During transient thermal operation ofthe heat exchanger, strain accumulates in the parting sheets separatingtwo heat transfer streams, adjacent to the open ends of the counter-flowfin segments. A global thermal deflection is created in the heatexchange matrix, while the cross-flow headers, experiencing little heattransfer, are strained through connection with the parting sheets whichextend from the matrix and connect the cross-flow headers to the heatexchange matrix. Along the interface between the matrix and thecross-flow headers there is also a local thermal gradient created by thedifference in heat transfer rate between the matrix and the cross-flowheaders. The resulting difference in transient temperature, and theattendant thermal strain, can be exacerbated by the difference instiffness between the matrix, the cross-flow headers and the interfacethereof. Strain accumulates in the softer cross-flow region where it maycause damage.

[0089] As best illustrated in FIG. 20, internal finned member 206 ispositioned offset from first and second external finned members 208,210, such that leading edges 234, 236 of first and second externalfinned members 208, 210 outwardly extend with respect to internal finnedmember 206 and partially cover a portion of the outlet header 229.Leading edges 234, 236 remain in general alignment with one another andin an offset alignment with trailing edge 228 of internal finned member206.

[0090] The outlet header 229 is a cross-flow, finned header. In anexemplary embodiment, the outlet header 229 is positioned between and isconnected to first and second parting sheets 202, 204. The outlet header229 is comprised of more coarsely configured fins than internal andexternal finned members 206, 208, 210. The outlet header 229 ispositioned adjacent to internal finned member 206 at trailing edge 228.The outlet header 229 is configured to collect an internal fluid frominternal finned member 206 and deliver the flow to outlet aperture 262.The outlet header 229 directs the flow of an internal fluid generallyalong the first plane in a third direction that is substantiallyperpendicular to the first direction.

[0091]FIG. 20 further illustrates the transition of the outlet header229 to the internal finned member 206, otherwise referred to astransition region 244. FIG. 21 illustrates the relative stiffness heatexchange cell 200 along the section of heat exchange cell 200illustrated in FIG. 20. FIG. 21 illustrates that the exemplaryembodiment of heat exchange cell 200, including the offset configurationof internal finned member 206 with respect to external finned members208, 210, significantly increases the stiffness of transition region244. The exemplary embodiment of FIG. 20, reduces damaging strainaccumulation by creating transition zone 244 including the offsetpositioning of first and second external finned members 208, 210 withinternal finned member 206 separated by first and second parting sheets202, 204. Transition zone 244 includes at least two significantcharacteristics over a non-offset configuration. First transition zone244 reduces the rate of heat transfer into first and second partingsheets 202, 204, and second, the structural stiffness of transition zone244 is significantly increased. These characteristics enable heatexchange cell 200 to exhibit lower thermal strain in operation andtherefore, increase the fatigue life of heat exchange cell 200.

[0092] The above disclosure describes only certain preferred embodimentsof a heat exchanger and is not intended to limit the scope of thepresent invention to the exact construction and operation shown anddescribed herein. The foregoing is considered to merely illustratecertain principles of the invention. Thus, it should be evident to thoseskilled in the art that numerous modifications and changes may be madeto the embodiments shown herein while remaining within the scope of thepresent invention as described and claimed.

What is claimed is:
 1. A heat exchanger for transferring heat between anexternal fluid and an internal fluid, the heat exchanger comprising: aplurality of heat exchange cells positioned in a stacked configurationwith respect to each other, each cell being connected to at least oneadjacent cell, each cell including: a first parting sheet includingopposing first and second surfaces, a first inlet header portion, afirst outlet header portion, a first internal finned member portion andperipheral edges; a second parting sheet substantially superimposed by,spaced apart from and coupled to the first parting sheet, the secondparting sheet including opposing third and fourth surfaces a secondinlet header portion, a second outlet header portion, a second internalfinned member portion and peripheral edges, the fourth surface of thesecond parting sheet confronting the second surface of the first partingsheet, at least a portion of the peripheral edges of the first andsecond parting sheets attached to each other; an internal finned memberdisposed between the second and fourth surfaces of the first and secondparting sheets, respectively, the internal finned member positioned atthe first and second internal finned member portions of the first andsecond parting sheets, respectively, and having a leading edgepositioned adjacent to the first and second inlet header portions of thefirst and second parting sheets, respectively, and a trailing edgepositioned adjacent to the first and second outlet header portions ofthe first and second parting sheets, respectively; at least one externalfinned member being attached to at least one of the first surface of thefirst parting sheet and the third surface of the second parting sheet,the external finned member having a leading edge and a trailing edge,the external finned member positioned such that the leading edge of theexternal finned member outwardly extends beyond the trailing edge of theinternal finned member.
 2. The heat exchanger of claim 1 , furthercomprising inlet and outlet finned members disposed between and attachedto the inlet and outlet header portions, respectively, of the first andsecond parting sheets.
 3. The heat exchanger of claim 1 , wherein theinternal finned member is configured to direct the flow of a fluidgenerally along a first path in a first direction and the inlet headerportions of the first and second parting sheets are configured to directthe flow of the fluid generally along a second path in a seconddirection substantially perpendicular to the first direction.
 4. Theheat exchanger of claim 3 , wherein the outlet header portions of thefirst and second parting sheets are configured to direct the flow of thefluid generally along a third path substantially perpendicular to thefirst path.
 5. The heat exchanger of claim 1 , wherein the at least oneexternal finned member is two external finned members, a first externalfinned member attached to the first surface of the first parting sheetand a second external finned member attached to the third surface of thesecond parting sheet.
 6. The heat exchanger of claim 3 , wherein eachexternal finned member is configured to direct the flow of a secondfluid in a direction generally opposite the first direction.
 7. The heatexchanger of claim 1 wherein the external finned members of adjacentheat exchange cells are connected together.
 8. The heat exchanger ofclaim 1 wherein the peripheral edges of the first and second partingsheets of each heat exchange cell further extend and connect to adjacentheat exchange cells.
 9. A heat exchange cell of a heat exchanger fortransferring heat between an external fluid and an internal fluid, theheat exchange cell comprising: a first parting sheet including opposingfirst and second surfaces, a first inlet header portion, a first outletheader portion and a first internal finned member portion; a secondparting sheet substantially superimposed by, spaced apart from andcoupled to the first parting sheet, the second parting sheet includingopposing third and fourth surfaces, a second inlet header portion, asecond outlet header portion and a second internal finned portion, thefourth surface of the second parting sheet confronting the secondsurface of the first parting sheet; an internal finned member disposedbetween the first and second parting sheets, at the first and secondinternal finned member portions, the internal finned member having aleading edge and a trailing edge; at least one external finned memberbeing attached to at least one of the first surface of the first partingsheet and the third surface of the second parting sheet, the externalfinned member having a leading edge and a trailing edge; an outletheader connected to the first and second outlet header portions of thefirst and second parting sheets, respectively, the trailing edge of theinternal finned member extending along the juncture of the first andsecond outlet header portions to the first and second internal finnedmember portions of the first and second parting sheets, respectively;and an inlet header connected to the first and second inlet headerportions of the first and second parting sheets, respectively, theleading edge of the internal finned member extending along the junctureof the first and second inlet header portions to the first and secondinternal finned member portions of the first and second parting sheets,respectively, the external finned member positioned offset from theinternal finned member such that the leading edge of the external finnedmember outwardly extends beyond the trailing edge of the internal finnedmember.
 10. The heat exchange cell of claim 9 , wherein the inlet andoutlet headers are cross-flow headers.
 11. The heat exchange cell ofclaim 9 , wherein the inlet and outlet headers each further include afinned member.
 12. The heat exchange cell of claim 9 , wherein theinternal finned member is configured to direct the flow of a fluidgenerally along a first plane in a first direction and the inlet headeris configured to direct the flow of the fluid generally along the firstplane in a second direction substantially perpendicular to the firstdirection.
 13. The heat exchange cell of claim 9 , wherein the internalfinned member is configured to direct the flow of a fluid generallyalong a first axis and the outlet header is configured to direct theflow of the fluid generally along a third axis substantiallyperpendicular to the first axis.
 14. The heat exchange cell of claim 9 ,wherein the leading edge of the at least one external finned member ispositioned over the outlet header.
 15. The heat exchange cell of claim 9, wherein the at least one external finned member is two external finnedmembers, a first external finned member attached to the first surface ofthe first parting sheet and a second external finned member attached tothe third surface of the second parting sheet.
 16. The heat exchangecell of claim 9 , wherein the first and second parting sheets furtherinclude peripheral edges and at least a portion of the peripheral edgesof the first and second parting sheets are attached to each other. 17.The heat exchange cell of claim 16 , wherein the first and secondparting sheets define a high pressure chamber and the internal finnedmember is disposed within the chamber.
 18. The heat exchange cell ofclaim 12 , wherein each external finned member is configured to directthe flow of a second fluid in a direction generally opposite the firstdirection.
 19. The heat exchanger of claim 11 the finned member of theinlet and outlet headers each include convolutions.
 20. The heatexchanger of claim 9 wherein the internal finned member is connected tothe second surfaces of the first and second parting sheets.